Interface StepHandler

This interface represents a handler that should be called after
each successful step.

The ODE integrators compute the evolution of the state vector at
some grid points that depend on their own internal algorithm. Once
they have found a new grid point (possibly after having computed
several evaluation of the derivative at intermediate points), they
provide it to objects implementing this interface. These objects
typically either ignore the intermediate steps and wait for the
last one, store the points in an ephemeris, or forward them to
specialized processing or output methods.

handleStep

interpolator - interpolator for the last accepted step. For
efficiency purposes, the various integrators reuse the same
object on each call, so if the instance wants to keep it across
all calls (for example to provide at the end of the integration a
continuous model valid throughout the integration range, as the
ContinuousOutputModel class does), it should build a local copy
using the clone method of the interpolator and store this copy.
Keeping only a reference to the interpolator and reusing it will
result in unpredictable behavior (potentially crashing the application).